gpL115 is a major T lymphocyte surface glycoprotein. It is deficient and/or defective in lymphocytes of patients with the X-linked lymphocyte/platelet defect Wiskott-Aldrich syndrome (WAS). Normal gpL115 has been purified from a lymphoblastoid cell line and the amino acid and carbohydrate compositions have been determined. gpL115 is a heavily glycosylated, sialic acid- bearing, rod-like, surface glycoprotein with physicochemical relatedness to GPIb of platelets and to glycophorin of erythrocytes. Evidence is presented which suggests that gpL115 functions to assure the survival of normal lymphocytes in the circulation and that defective gpL115 in the WAS leads to accelerated lymphocyte senescence and resultant immunodeficiency. The proposal aims to define the structure of normal gpL115 (composition, sequence and conformational states). The structural information will be used to test the hypothesized function, and to define the nature and consequences of the defect in gpL115 molecules in WAS lymphocytes. We will complete the compositional analysis, define major carbohydrate moieties and describe domains. Polypeptide fragments will be generated and partial amino acid sequence determined so that oligonucleotide probes can be synthesized. gpL115 clones will be selected from a cDNA library using oligonucleotide hybridization and screening with anti- protein antibodies. The DNA will be sequenced and the amino acid sequence of gpL115 deduced and analyzed. The cDNA will be used as a probe to establish the chromosomal location of the gpL115 gene, an important questions since the WAS is an X- linked defect. If the gpL115 gene is on the X-chromosome, its mRNA, cDNA and gene will be examined in WAS patients and families. The biosynthesis and stability of gpL115 will be compared in WAS and normal lymphocytes. We will examine the conformation of native and sialidase-treated gpL115 by electron microscopy and by the use of conformation-specific antibodies to determine whether the removal of sialic acid residues changes gpL115 from a rod-like conformation which "masks" senescence antigens to a globular conformation inappropriate for the masking function. We will determine whether the defective gpL115 molecules on WAS lymphocytes have the globular conformation. The hypothesized function of gpL115 in controlling senescence will also be tested by quantifying IgG molecules bound to the surface of normal lymphocytes, sialidase- treated lymphocytes and WAS lymphocytes.